# Intensity of the incident light

1. Apr 5, 2009

### vrobins1

1. The problem statement, all variables and given/known data

Unpolarized light is incident on a system of three polarizers. The second polarizer is oriented at an angle of 33.0° with respect to the first and the third is oriented at an angle of 45.0° with respect to the first. If the light that emerges from the system has an intensity of 2.3 W/m2, what is the intensity of the incident light?

2. Relevant equations

Iout=Iincos2$$\theta$$

3. The attempt at a solution

I know that after I0 passes through the first polarizer, it is 1/2I0. After it passes through the second, I thought it would be 1/2I0cos2(33), and after it passes through the third, 1/2I0cos2(33)cos2(45).
This would all equal 2.3, which I was given.
So I set up my final equation as:
1/2I0cos2(33)cos2(45) = 2.3, or
I0= 2.3 / (1/2cos2(33)cos2(45).

I solved and got 13.08, but that is incorrect. Can anyone offer any insight? Thanks.

2. Apr 6, 2009

### Redbelly98

Staff Emeritus
For the third polarizer, use the angle between it and the second polarizer.

45° is the angle between the third and first polarizer.